Time

Every sad or every happy event is a point in time. A point in time
that passes never to come back again.

True happiness, is eternal, and hence not bound to time. All the
events that happen in your life don't make you happy or sad. You're
either happy or sad doing them, outside of time.

So, choose to be happy, and not let your happiness be bounded to the
moment.

Be happy because you are not bound by time.